What is a catalyst that could be used as an aqueous solution, so that it's phase could be manipulated without having to use extreme tempretures?
A Cobalt cyano complex [CoH(CN)5]˄3- is a well known water soluble catalyst for the regioselective hydrogenation of dienes to monoenes in homogeneous aqueous solutions, e.g. hydrogenation of 2,4-hexadienoic acid or sorbic acid. Another example of huge chemical and industrial relevance is the C-C bond formation reactions through hydroxymethylation of silyl enol ethers with formaldehyde (and other aldehydes) that has been accomplished using a range of lanthanide triflates Ln(OTf)3, in aqueous phase. There are thousands of examples of important organic syntheses being carried out in aqueous solutions now. As expected, product separation and recycling of catalyst becomes quite easier when one uses water as the reaction medium. To top it all, the environmental benefits that are usually associated with aqueous phase reactions make these protocols (and the corresponding organometallic catalysts) really attractive.